1. Field Of The Invention
The invention relates to processes for establishing a common fracture network interconnecting a plurality of wells.
2. Description Of The Prior Art
Numerous processes involve the establishment of a common flow network connecting a plurality of wells intersecting an underground formation.
One example of such a process is a steamflood process for enhancing the production of hydrocarbons, particularly in situations involving heavy viscous hydrocarbon deposits Also, such techniques of establishing a common fracture network have application in solution mining.
Often, the well-to-well communication network is created by hydraulically induced fracturing of the subsurface formation.
One such prior art technique is disclosed in U.S. Pat. No. 3,990,514 to Kreinin et al. The Kreinin et al. patent discloses a method for connection of wells in the underground gasification of coal beds. In that technique, a fracture is propagated between a first and second well by pumping injection fluid under pressure into the second well while closing the first well and simultaneously opening any other surrounding wells. This creates a hydraulic fracture directed from the second well into communication with the first well. To subsequently connect a third well to the fracture network previously created between the first and second wells, injection fluid is pumped into the third well while closing in the second well and opening the first well and any other surrounding wells. This causes a fracture to initiate at the third well and travel back to the second well, presumably into substantial communication with the first created fracture. Thus, the Kreinin et al. disclosure does not disclose the successive propagation of an initial fracture from well to well, but rather it initiates new fractures at subsequent wells and propagates them back into communication with the existing fracture.
The Kreinin et al. patent discloses a technique for creating the fracture substantially adjacent the lower boundary of a formation. This is accomplished by casing the wells to a point shortly above the lower boundary of the formation, thus leaving an uncased portion of the well adjacent the lower boundary of the formation. Thus, the fracture system is created between these uncased portions of the wells which are located relatively near the lower boundary of the formation. The Kreinin et al. patent also discloses an example in which the subsurface formation was inclined or tilted relative to the ground surface, but this inclination was apparently only incidental, and was not utilized to control the location of the hydraulically created fracture.
One particular type of process in which the formation of a well-to-well flow communication network between a plurality of wells is important, is a fracture-assisted steamflood process developed by the assignee of the present invention as disclosed in U.S. Pat. No. 4,265,310 to Britton et al. As disclosed in the Britton et al. patent, one of the significant features of this fracture-assisted steamflood process is that a central injection well of a steamflood pattern is connected to the associated surrounding production wells by a fracture through which steam is injected at rates sufficient to maintain the fracture in parted condition.
In the Britton et al. process, a single fracture is initiated at the central injection well and propagated radially outward in all directions therefrom to intersect each of the outlying production wells in a typical well pattern such as an inverted five-spot, seven-spot or nine-spot pattern. Since each production well will typically be associated with more than one injection well, the fractures initiated at the injection wells may be communicated with each other, particularly in the permeable zones created immediately adjacent the production wells. Again, however, as was the case with the Kreinin et al. '514 patent, the overall fracture network which may intercommunicate the field is not created by the continuous propagation of a single fracture; instead, multiple independently initiated fractures are connected together.